The present invention pertains to power-assist parallel hybrid vehicles. More specifically, the present invention pertains to a dual-structured power output apparatus that provides a means for outputting both mechanical power and electrical power with high efficiency and is capable of improving fuel efficiency of the prior art hybrid vehicle, as well as to an electric drive and power system and a method of controlling the power output apparatus.
In recent years, the trend in the development of fuel-efficient and low emission hybrid vehicle powertrain technologies that combine a conventional combustion engine (ICE) with an electric propulsion system has increased significantly. Among the roughly four main categories: series, parallel, series-parallel and mild hybrid vehicle technologies on the market today, the mild hybrid technology is the least expensive and affordable. The technology is relatively less complex and can be readily retrofitted into an existing conventional vehicle with little or no modifications. It involves replacing the conventional alternator with an over-sized belt-driven electric motor that is commonly referred to as a Belt Alternator Starter (BAS). The motor is coupled to the engine via a serpentine belt so that it serves as both a generator and starter. This permits a low-cost method of adding hybrid capabilities to a conventional vehicle, such as start-stop function as well as mild levels of torque assist and regenerative braking efficiency-improvement technology, that achieves about 15-20 percent improvement in fuel economy in urban driving.
However, the authors of the present invention have recognized a number of functional drawbacks with the current state-of-the-art in belt-driven electric motor as typically utilized in mild hybrid vehicle powertrain technology on the market today. One functional drawback is that using a single electric motor makes it necessary for frequent mode reversals because it can operate only in one mode (motoring or generating) at a time, and this results in reduced powertrain performance and fuel efficiency. Typically, the electric motor operates in a limited mechanical torque- and power-assist modes for shorter durations and generating mode producing electrical power for longer durations in order to avoid depleting the onboard energy storage devices (super-capacitors and battery bank) of a hybrid vehicle. This operating limitation results in smaller improvement in fuel efficiency.
Another functional drawback of the current state-of-the-art in belt-driven electric motors as utilized in mild hybrid vehicle powertrain technology is that they are typically optimized for one of the operating modes than the other. Therefore, in a hybrid powertrain that has such an electric motor mounted thereon, in a time period when the power demand requires the electric motor to operate in its less optimized mode, a reduced powertrain performance and fuel efficiency are achieved.
Yet another functional drawback of the current state-of-the-art in belt-driven electric motors as utilized in mild hybrid vehicle powertrain technology is that the electric motors are typically sized based on the peak power. As a result, they are relatively over-sized, heavier and less efficient in the power range corresponding to the average power demand of the drive cycle. This is done in order to be able to support start-stop features during engine idle, regenerative braking during stopping and coasting, and engine mechanical power boosting and augmentation for transient power requirements. Therefore, in a vehicle that has such an electric motor mounted thereon, in a time period when the vehicle power demand in accordance with the driving conditions requires the electric motor to operate close to the average power demand, a reduced electric motor performance and fuel efficiency are achieved.
A number of prior arts, for example U.S. Pat. No. 8,412,396, U.S. Pat. No. 5,943,918, U.S. Pat. No. 8,225,608, US2005/0107198, US2004/0040810 A1, U.S. Pat. No. 7,753,147, U.S. Pat. No. 7,914,416, US2013/0005529 A1, have described a variety of hybrid vehicles comprising single and dual electric motor-generators. However, all of these prior art patents do not address any of the drawbacks discussed above in order to improve fuel efficiency of a belt-driven parallel hybrid vehicle. The apparatus disclosed in the present invention differs significantly from those disclosed in the prior arts in terms of its characteristics and method of control.
Furthermore, no prior art in hybrid vehicle powertrain technologies and conversion of conventional vehicle into hybrid that use belt-driven electric motors coupled to the engine crankshaft via a special belt has provided solutions that address the functional drawbacks discussed above in order to achieve improvement in fuel efficiency.
Accordingly, there is a need for a simple, cost-effective and affordable hybrid vehicle powertrain technology solution that provides further improvement in fuel efficiency of the prior art mild hybrid vehicle.